AGE AND GROWTH OF THE CISCO 
249 
The equations show that both the males and females of the Clear Lake cisco grow 
more rapidly in depth and width than in length. The differential growth of the 
dimension, width, proceeds more rapidly than the differential growth of the dimen- 
sion, depth, that is, the change to a heavier stature proceeds more rapidly along the 
lateral than along the vertical axis. The comparison of the equations for the two 
sexes shows further that the differential growth in depth proceeds at approximately 
the same rate in the males and the females, while the differential growth in width 
proceeds more rapidly in the females than in the males. It is this higher differential 
growth in width that accounts for the higher K values in the Clear Lake females. 
Values of K for cisco populations have been presented by Van Oosten (1929) 
and by Hile (1931). The former author found K to have an average value of 1.13 
for the Lake Huron herring (0.01126 in his method of presentation). The sexes 
showed no consistent differences, and there was only a slight tendency for the value 
of K to increase with increase in length. Hile’s data on the cisco of the Indian 
Village Lakes (Indiana) were too scanty to afford any information on the change in 
the value of K with change in length. The largest value of K which he found for any 
age group was 1.79, the smallest, 1.56. Since both Van Oosten and Hile employed 
the cube relationship for the calculation of K values, their results can be compared 
directly with those of this study. 
A comparison of the values of K in the Lake Huron herring and the Indian 
Village Lakes cisco with those of the populations of this study shows that the Lake 
Huron herring is a very slender fish of approximately the same relative heaviness as 
the Muskellunge Lake cisco, while the Indian Village Lakes cisco is more heavily 
built than the Trout Lake, Muskellunge Lake, and Silver Lake ciscoes, but slighter 
in form than the Clear Lake cisco. 
LENGTH OF GROWING SEASON 
It was not possible in this investigation to follow the course of the season’s 
growth in the different populations by means of a systematic collection of specimens 
at different times throughout the spring, summer, and autumn. Since all collec- 
tions were made in July, August, and early September, and the single year’s collec- 
tions within a single lake were frequently made within a period of only a few days, 
any estimate of the course of growth during the growing season or of the length of the 
growing season in the different lakes must depend largely upon an indirect approach. 
However, the fact that the growth materials from each lake represent collections in 
2 or more years makes possible at least a rough estimate of the length of the growing 
season in each lake. The following example will illustrate the method by which these 
estimates may be made: 
The 1928 collection of the Trout Lake cisco contained 102 specimens of the II 
group (1926 year class). These fish had an average length of 134 millimeters at the 
time of capture (July 21, 28, and 29). The calculation of their earlier growth from 
scale measurements indicated that their average length at the beginning of the 
1928 growing season (end of second year of life) was 117 millimeters. Thus it may 
be seen that these II-group fish of 1928 had grown 17 millimeters between the begin- 
ning of the growing season and the time of their capture in late July. The question 
now arises as to what part of the total 1928 growth of the II group this 17-millimeter 
increment may represent. The presence of this same (1926) year class in the 1930 
collections as the IV group and in the 1931 collections as the V group makes a quite 
reliable answer to this question available, for it is possible to calculate the total 
24535—36 4 
